Tests failing on Nightly Python builds

[jaraco]

Starting in this build, the tests seem to have started failing on the nightly builds, presumably due to a change in them.

[jaraco]

Recommendations from the upstream issue:

I think that it would be better to not depend on exact result of re.escape. Either use re.escape for calculating the part of the expected result that is out of your full control:

assert get_pattern(l('foo/bar')) == l(re.escape('foo/bar') + r'\Z(?ms)')

Or test the pattern indirectly. For example, it should match 'foo/bar', but not 'foo/bar\n'.

Note that compiling the pattern r'foo/bar\Z(?ms)' emits a deprecation warning in 3.6+ since flags are not at the start of the expression. It is worth to rewrite get_pattern() until it become an error.